Enter a value for the ratio (Vout/Vin) to find the optimal resistor values that yield the specified division ratio. You can optionally enter a value for R1 or R2 with the ratio if you want to fix the value of one of the resistors. Entering both R1 and R2 will calculate the ratio. If over specified (R1, R2, and the ratio are entered), the ratio value is ignored. Note that the ratio must always be less than 1.

Resistive voltage dividers may be one of the most common circuit configurations used. In most cases, voltage dividers are used to derive a voltage from a fixed input level. In some case, such as scaling a signal level for input to an ADC or amplifier, it is more convenient to think of the ratio, or the magnitude that the input is reduced by to produce an output, than absolute voltage level. If you are interested in absolute voltage levels, use the “Single Supply” or “Dual Supply” solvers in the “Dividers” category.

As is the case with all resistive voltage dividers, placing a load on Vout will change the output level. Unless Vout is very lightly loaded (for instance the input of a non inverting op-amp or other high impedance load) you may need to buffer its output first. If you wish to lower the resistances found to minimize loading effects, one convenient strategy is to divide the value of R1 and R2 by ten. The resulting values will still be standard values in the original tolerance.

This solver uses the following equation to compute its values.